1. Technical Field
This application relates to computer storage devices, and more particularly to the field of transferring data between storage devices.
2. Description of Related Art
Computer systems may include different resources used by one or more host processors. Resources and host processors in a computer system may be interconnected by one or more communication connections. These resources may include, for example, data storage devices such as the Symmetrix™ family of data storage systems manufactured by EMC Corporation. These data storage systems may be coupled to one or more host processors and provide storage services to each host processor. An example data storage system may include one or more data storage devices, such as those of the Symmetrix™ family, that are connected together and may be used to provide common data storage for one or more host processors in a computer system.
A host processor may perform a variety of data processing tasks and operations using the data storage system. For example, a host processor may perform basic system I/O operations in connection with data requests, such as data read and write operations.
Host processor systems may store and retrieve data using a storage device containing a plurality of host interface units, disk drives, and disk interface units. Such storage devices are provided, for example, by EMC Corporation of Hopkinton, Mass. and disclosed in U.S. Pat. Nos. 5,206,939 to Yanai et al., 5,778,394 to Galtzur et al., U.S. Pat. No. 5,845,147 to Vishlitzky et al., and U.S. Pat. No. 5,857,208 to Ofek. The host systems access the storage device through a plurality of channels provided therewith. Host systems provide data and access control information through the channels to the storage device and storage device provides data to the host systems also through the channels. The host systems do not address the disk drives of the storage device directly, but rather, access what appears to the host systems as a plurality of logical disk units. The logical disk units may or may not correspond to the actual disk drives. Allowing multiple host systems to access the single storage device unit allows the host systems to share data stored therein.
A backup copy of one or more of the actual devices, or portions thereof, may be maintained. Different techniques may be used in connection with providing a backup copy of data. Backup copies may be made on disks using a log or journal file of changes made with reference to a specific point-in-time copy of the data. One drawback with existing techniques is that a duplicate copy of the data may be used as the specific point-in-time copy. Also, there may be contention with reference to the journal or log file, for example, when in use by multiple hosts performing write operations. Maintaining the journal or log file may also be expensive in terms of execution time required to performing the write operation to the journal or log file.
Thus, it may be desirable to use a technique that provides a continuous backup of data while overcoming one or more drawbacks of the existing techniques. It may be desirable to use a technique which provides a continuous backup of data while reducing contention and execution time associated with performing a journaling or logging operation. It may be desirable to use a technique which provides a copy of the data without using a duplicate copy of the data such as with reference to a complete point-in-time copy of the data.